A model to study soliton propagation characteristics in nonlinear transmission lines (NLTLs) periodically loaded with voltage dependent capacitances is presented. This is based on the LC ladder equivalent network of the NLTL, and can be applied to structures where the Korteweg-de Vries approach does not hold. Specifically, the model allows to numerically obtain soliton waveforms under arbitrary capacitance non linearity. To demonstrate its validity, it has been applied to structures loaded with symmetric capacitances, similar to those exhibited by actual heterostructure barrier varactors. The model can be of help to understand harmonic generation in monolithic NLTL-based frequency multipliers. © 2001 American Institute of Physics.